Abstract
The kinetics of oxidation of iota- and lambda-carrageenans by permanganate ion in alkaline solutions have been investigated, spectrophotometically. Kinetic and spectrophotometric evidences revealed the formation of intermediate complexes involving short-lived manganate (VI) and/or hypomanganate (V) transient species. The products were identified by IR spectroscopy and elemental analysis as corresponding keto-acid oxidation derivatives.
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▶ The kinetics and mechanistics of oxidation of some sulfated macromolecules by alkaline permanganate. ▶ Novel synthesis of keto-acid derivatives of iota- and lambda-carrageenans by oxidation processes. ▶ Spectrophotometric detection of short-lived Mn
V and Mn
VI intermediates using a conventional spectrophotometer. ▶ Behavior of sulfated polysaccharides in aqueous alkaline solutions.
The kinetics of formation of intermediate complexes during the oxidation of iota- and lambda-carrageenan sulfated polysaccharides (CAR) as natural polymers by alkaline permanganate at pH's ≥12 have been investigated using a conventional spectrophotometer. The reactions showed first-order dependences in permanganate and fractional-first-order kinetics with respect to carrageenans concentration. Kinetic and spectrophotometric evidences revealed the formation of intermediate complexes involving green manganate (VI) and/or blue hypomanganate (V) short-lived transient species. The influence of pH on the oxidation rates indicated that the formation of complexes is base-catalyzed. The kinetic parameters have been evaluated and mechanisms consistent with the experimental results are discussed.